Home Extension L1b Calculations

Pre 2021 Regulation Version

The Area-Weighted U-Value Method

If the extension fails the reference method, the Area-Weighted U-Value Method is a second option for demonstrating compliance.

Under this method, the overall area-weighted U-value of the extension and glazing should be lower than a Notional Extension of the same size and shape that meets the Reference Method’s specifications.

We have provided the following tool to help Architects and Homeowners comply with extensions.
If your extension fails due to being heavily glazed, we can complete a Whole Dwelling Calculation to take into account other upgrades to your home as part of the works.